1. Technical Field
The present disclosure relates to a semiconductor memory device and, more particularly, to a semiconductor memory device having two different memory areas, such as a RAM area and a ROM area, in one chip.
2. Discussion of Related Art
As portable electronic devices become more widely used with the development of the information technology (IT) industry, there is an increasing demand for a nonvolatile memory device for use as a main memory for electronic devices and equipment, such as portable computers, cellular phones, and game machines, which have file storing and retrieving functions, or as a recording medium for recording voice or images. This kind of nonvolatile memory device has an advantage in that it does not lose stored information, even when the power is turned off. Examples of such a nonvolatile memory device include an electrically-erasable programmable read-only memory (EEPROM), a flash memory, a ferroelectric random access memory (FRAM), a phase change random access memory (PRAM), and a magnetic random access memory (MRAM).
In a modern portable terminal such as a cellular phone, a personal communications services (PCS) phone, or an international mobile telecommunication (IMT) phone, demands for additional functions such as data communication, telephone number database, schedule management, personal memo, broadcasting program reception, and moving picture/music playback, as well as basic voice communication are increasing. These demands increase the size of a control application program installed in the portable terminal.
FIG. 1 is a schematic block diagram illustrating a system such as a portable terminal having several types of memories.
As shown in FIG. 1, in the portable terminal, memories may be generally divided into read only memories (ROMs) 20a and 20b storing a control program for controlling the operation and function of the portable terminal, and random access memories (RAMs) 30a and 30b for executing the control program.
The ROMs 20a and 20b and the RAMs 30a and 30b are controlled by a controller 10. For example, the controller 10 inputs an external address XADD, external data XIO, and a control signal XCTRL to the ROMs 20a and 20b and the RAMs 30a and 30b so that the data is written to a prescribed area. Further, when data is read from a prescribed area, the controller 10 applies the external address XADD and the control signal XCTRL and outputs read data to the exterior.
The ROMs can be electrically erasable programmable read-only memories (EEPROM) or flash memories and have a nonvolatile characteristic. Such ROM's, however, show low write operation speed and accordingly are mainly used for a read operation. The RAMs are cache memories supplementing the ROMs. For example, a static random access memory (SRAM) is widely used.
As the portable terminal having the above structure gets smaller, an occupying area available for the memories in the portable terminal is reduced. According to this trend, a multi-chip package (MCP) technique for packaging several chips as one entity has been developed. In FIG. 1, a memory combination 40, including the ROMs 20a and 20b and the RAMs 30a and 30b, generally has such an MCP structure.
When two or more memories are used, however, a structure of the memory combination gets complicated and such memories need to be separately driven. Accordingly, power consumption becomes significant and the cost increases. In addition, there is a difficulty in controlling several memory devices.